Polyimide-Based Membrane Materials for CO₂ Separation: A Comparison of Segmented and Aromatic (Co)polyimides

Area of Science:

• Polymer Science
• Materials Science
• Chemical Engineering

Background:

• Development of advanced materials for gas separation is crucial for industrial applications.
• Poly(ethylene oxide) (PEO)-based copolyimides offer tunable properties for membrane-based separations.
• Understanding the structure-property relationships in these materials is key to optimizing performance.

Purpose of the Study:

• To synthesize and characterize novel PEO-based copolyimides with varying hard segment structures.
• To investigate the effect of hard segment chemistry on CO2 selective separation properties.
• To compare the performance of copolyimides with their fully aromatic polyimide analogues.

Main Methods:

• Synthesis of copolyimides using aromatic dianhydrides (ODPA, 6FDA) and diamines (ODA, IPrDA, 4MPD) with constant PEO content.
• Comprehensive material characterization using techniques like 1HNMR, FTIR, WAXD, DSC, TGA, and AFM.
• Gas transport property measurements (permeability and selectivity) for various gases (He, O2, N2, CO2) under different pressure conditions.

Main Results:

• OPDA-ODA-PEO demonstrated the highest CO2 permeability (52 Barrer) and CO2/N2 selectivity (63) among the copolyimides.
• 6FDA-4MPD-PEO showed the second-best performance, with significantly lower permeability but still notable selectivity.
• The PEO-containing copolyimides generally outperformed their fully aromatic counterparts in terms of CO2 permeability.

Conclusions:

• The hard segment structure significantly influences the gas transport properties of PEO-based copolyimides.
• Partial filling of voids by PEO segments and imperfect phase separation are proposed mechanisms for the observed properties.
• These novel copolyimides represent promising candidates for efficient CO2 separation membranes.